Reverse Micelle Method Research Articles

Light‐Induced Stored Information in Nanoparticles

AbstractWe investigate here the consequence on light‐induced and thermally induced spin‐crossover (SCO) properties with particle size reduction from the macroscopic to microscale to nanoscale domains. Three samples with distinct particle sizes of the SCO coordination polymer [Fe(NCS)2(bpe)2] [bpe = 1,2‐bis(4′‐pyridyl)ethane] have been prepared by water‐in‐oil reverse micelle methods. Comparison of the magnetic properties with particle size reduction of these and the original macroscale slow‐grown crystals revealed that the spin transition becomes more gradual, more incomplete and concomitantly the transition temperature (T1/2) decreases – much like what is observed in metal dilution studies. Importantly, here, in the first photoinduced magnetic studies on a nanoparticle SCO system, we see that even on the nanoscale photoconversion of the low spin species to a metastable high‐spin state is possible. Furthermore, particle size reduction appears to have little effect on the temperature at which the stored photomagnetic information is erased. These results highlight that light‐induced SCO properties are governed by direct metal coordination environment (i.e., on the molecular scale), whereas, thermally induced magnetic properties rely more on crystal packing and ligand field effects.

Glucose oxidase-doped magnetic silica nanostrutures as labels for localized signal amplification of electrochemical immunosensors

Herein, we report a novel glucose oxidase (GOD)-doped magnetic silica nanostructure and its possible application in the clinical immunoassays. The doped nanostructures were initially synthesized using the reverse micelle method, and ferritin antibodies (anti-Ft) were then labeled to the surface of the nanostructures, which were employed as signal antibodies for ultrasensitive detection of ferritin (Ft) in the sandwich-type electrochemical enzyme immunoassays. The doped nanostructures were characterized using transmission electron microscopy (TEM), UV-vis absorption spectrometry and vibrating sample magnetometer (VSM). The advantages of the doped nanostructures as labels were investigated in comparison with the conventional label method. Under the optimal conditions, the nanostructures-based immunoassay toward ferritin standards displays a wide dynamic range from 0.1 to 400 ng mL(-1) with a low detection limit of 10 pg mL(-1) ferritin (at 3sigma), which is three-fold higher in the sensitivity than that of directly using GOD-labeled antibodies. The assay results for clinical serum samples with the developed method received in excellent accordance with results obtained from the referenced standard enzyme-linked immunosorbent assay (ELISA) method.

Structural optimization of gas diffusion electrodes loaded with LaMnO3 electrocatalysts

In this study, gas diffusion electrodes (GDEs) with two catalyst layers were fabricated and tested for their electrode performance for oxygen reduction in an alkaline solution. The LaMnO3/carbon black catalyst layers were fabricated using a reverse micelle method to finely disperse the LaMnO3 particles onto the carbon matrices, for which commercial Ketjen Black (KB) (1270 m2 g−1) and Vulcan XC-72R (VX) (254 m2 g−1) were used. The three-layer-structured GDE with the two LaMnO3/KB and LaMnO3/VX catalyst layers exhibited a superior oxygen reduction activity when compared to that of a conventional GDE with only one LaMnO3/KB catalyst layer. Pore size distribution and gas permeability measurements revealed that the LaMnO3/VX layer was more porous and had higher gas permeability than the LaMnO3/KB layer. These results suggest that the intermediate layer of LaMnO3/VX can efficiently supply oxygen to reaction sites dispersed in the LaMnO3/KB and LaMnO3/VX catalyst layers, which consequently leads to an improvement in the electrode performance.

Characterization of silica-coated silver nanoparticles prepared by a reverse micelle and hydrolysis–condensation process

Described herein is the synthesis of individually silica-coated silver nanoparticles using a reverse micelle method followed by hydrolysis and condensation of tetraethoxysilane (TEOS). The size of a silica-coated silver nanoparticle can be controlled by changing the reaction time and the concentration of TEOS. By maintaining the size of a silver nanoparticle as a core particle at around 7 nm, the size of a silica-coated silver nanoparticle increased from 13 to 28 nm as the reaction time increased from 1 to 9 h due to an increase in silica thickness. The size of silica-coated silver nanoparticles also increased from 15 to 22 nm as the TEOS concentration increased from 7.8 to 40 mM. The size of a silica-coated silver nanoparticle can be accurately predicted using the rate of the hydrolysis reaction for TEOS. Neither the dispersion nor the film of silica-coated silver nanoparticles exhibited any peak shifting during surface plasmon resonance (SPR) at around 410 nm, whereas, without silica coating, the SPR peak of Ag film shifted to 466 nm.

Size-controlled synthesis of CuO–ZrO2 nanoparticles prepared through reverse micelle method

In this research, CuO–ZrO2 nanoparticles are synthesized using microreactors made of surfactant/water/cyclohexane microemulsions. The effect of different microemulsion variables on the particle size and its distribution, such as water-to-surfactant molar ratio (W0) and different surfactants are discussed. Three different surfactant types including cationic (CTAB), anionic (AOT), and nonionic (Brij56) are used. Also a different amount of water to surfactant in nano composite synthesis is used. The powders were characterized by DTA/TG, XRD, SEM, EDS, TEM and BET techniques and their physical properties are compared. The results show a decrease of particles size in presence of cationic surfactant. Narrow particles size distribution of the resultant CuO–ZrO2 nanocomposite in presence of cationic surfactant, anionic and nonionic surfactant is compared. Also for AOT surfactant, by raising water to surfactant molar ratio the particles size is increased and the optimum ratio is H2O: Surfactant = 0.32:0.055, respectively.

Optical properties of CdS and CdS/ZnS quantum dots synthesized by reverse micelle method

The CdS and CdS/ZnS semiconductor quantum dots have been synthesized by reverse micelle method using sodium bis (2-ethylhexyl) sulfosuccinate (AOT) surfactant agent. The quantum dot diameter is about 2.5 to 4 nm depending on the concentration of the surfactant agent. It is interesting that, in contrast to other colloidal methods, the size of quantum dots does not depend on the growth time. The absorption spectra of CdS quantum dots show the narrow size distribution. The photoluminescence (PL) spectra include two bands, the intrinsic emission of CdS nanocrystals and the emission of surface states. There is noticeable increase of the PL intensity and subsequent photostability of CdS/ZnS core-shell quantum dots in comparison with CdS quantum dots without the ZnS shell.

Synthesis of nanosilver particles by reverse micelle method and study of their bactericidal properties

Nanosilver particles have been synthesized by the reverse micelle method, where AgNO3 was used as a silver ions source, NaBH4 and quercetin – as reducing agents, CTAB, SDOSS and AOT- as surfactants, while the stabilizer was Vietnamese chitosan. Studying the factors influencing the process of nanosilver particle formation, it was shown that the particle size of the nanosilver products depends on the concentration of the reaction components and their stoichiometric ratio. It was also shown that the reaction system using AOT surfactant is capable of producing nanosilver particles with smallest nanoparticles (ϕav ∼ 5 nm) and good particle-size distribution. The study on bactericidal activity of the nanosilver products indicated that the disinfecting solution with a nanosilver concentration of 3 ppm was able to inhibit all E.coli and Coliforms, TPC and fungi at 15 ppm, while Vibrio cholerae cells were inactivated completely with 0.5 ppm of nanosilver after 30 minutes exposition.

The influence of the shell on magnetic properties of CdS: Mn/SiO2 composite nanoparticles

Silica-coated Mn-doped CdS nanocrystals were synthesized by use of a reverse-micelle method. Transmission electron microscopy, X-ray diffraction and electron paramagnetic resonance were adopted to characterize the samples, and their magnetic properties were studied via superconducting quantum interference device magnetometry. The samples exhibit anomalous ferromagnetic property at low temperature. The CdS: Mn nanocrystals dispersed in a silica matrix exhibit an obvious hysteresis loop shift toward the direction of the magnetic field; by contrast, the nanocrystals coated with compact SiO2 shell layers display a symmetric hysteresis loop. The shell layers are supposed to be responsible for the distinct magnetic behaviors.

Development of an enzyme activity screening system for β-glucosidase-displaying yeasts using calcium alginate micro-beads and flow sorting

Recent reports on high-speed affinity screening systems for yeast cells using flow cytometry have not been adapted to screening yeast cells that display hydrolyzing enzymes, since the fluorescent molecules which are released from fluoresceinated substrate diffuse into solution after enzymatic reaction. In this research, yeast cells displaying beta-glycosidase were individually captured in micro-sized calcium alginate beads by using the newly developed reverse micelle method to prevent diffusion of hydrolyzed fluorescent substrates. By adopting flow sorting to these captured cells, active cells were successfully enriched about 82-fold from a mixed suspension with negative controls. This system should be a useful method for high-speed screening of yeast cells that display various hydrolyzing enzymes and has potential application to screening randomized libraries of enzyme-displayed yeast cells with higher activities.

Fabrication of Nanoparticles of Barium Carbonate/Oxalate Using Reverse Micelle Technique

Nanoparticles of barium carbonate/oxalate have been synthesized in situ from barium nitrate and ammonium carbonate/oxalate by reverse micelle method. These particles were characterized using transmission electron microscope (TEM), fourier transform infrared (FTIR) and x-ray diffraction (XRD). The results indicate that rod-like barium carbonate (BaCO3) and spherical barium oxalate (BaC2O4) nanoparticles can be fabricated with high crystallinity.

Size-controlled synthesis of LaAlO 3 by reverse micelle method: Investigation of the effect of water-to-surfactant ratio on the particle size

Lanthanum monoaluminate (LaAlO 3) nanoparticles have been synthesized using microreactors made of poly(oxyethylene) nonylphenyl ether (Igepal CO-520)/water/cyclohexane microemulsions. The control of particle size was achieved by varying the water-to-surfactant molar ratio. The synthesized and calcined powders were characterized by thermogravimetry–differential thermal analysis (TGA-DTA), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Differential thermal analysis showed that LaAlO 3 phase transformation decreases with increase in water/surfactant ( R) value. Pure LaAlO 3 phase was synthesized by annealing at 800 °C for 2 h in air directly from amorphous precursors, without formation of intermediate phase. The average particle size was found to increase with increase in water-to-surfactant ratio ( R). FTIR analysis was carried to monitor the elimination of residual oil and surfactant phases from the microemulsion-derived precursor and calcined powder.

Cobalt Oxalate Nanoribbons as Negative-Electrode Material for Lithium-Ion Batteries

Orthorhombic cobalt oxalate dihydrate has been prepared in the form of nanoribbons by a reverse micelles method. The crystallographic structure of the resulting solid differs from the monoclinic massive product. A careful dehydration of the nanocrystals leads to anhydrous cobalt oxalate in which the nanoribbon-shaped particles are preserved and Co2+ ions are located in a centrosymmetric environment. CoC2O4 is used for the first time as high-capacity lithium storage materials with improved rate performance. The anhydrous solids react with lithium, leading to metallic cobalt and lithium oxalate, as shown by XAS and FTIR measurements. The new electrode material displays reversible capacities close to 900 mA·h·g−1 between 0 and 2 V versus lithium by a novel reaction mechanism which involves cobalt reduction−reoxidation.

Assembly and electroanalytical performance of Prussian blue/polypyrrole composite nanoparticles synthesized by the reverse micelle method

We report on the characterization, assembly and electroanalytical performance of Prussian blue/polypyrrole (PBPPy) composite nanoparticles synthesized by the reverse micelle method. Scanning electron microscopy suggests the formation of nanosized PBPPy particles with diameters between 40 and 50 nm. Optical absorption confirms that the particles are composed of Prussian blue (PB) and polypyrrole. PB and PBPPy nanoparticles were anchored onto the surface of cysteine-modified Au electrodes. Cyclic voltammetry experiments show that PB- or PBPPy-modified electrodes exhibit intrinsic electrochemical properties and a high electrocatalytic activity towards H2O2. PBPPy-modified electrodes exhibit a higher sensitivity to H2O2 than PB-modified electrodes. A linear calibration curve in the concentration range 0.99 μM–8.26 mM H2O2 is constructed with a detection limit of 0.23 μM at a signal-to-noise ratio of 3. Excellent stability is observed for PBPPy-composite-nanoparticle-modified electrodes even in a pH 6 phosphate buffer solution with a high H2O2 concentration (0.99 mM). Glutaraldehyde and were also employed to immobilize glucose oxidase for the development of PBPPy-based biosensors. The results show that PBPPy composite nanoparticles can be used to develop oxidase-based biosensors.

Synthesis and Effect of Some Parameters through Reverse Micelles Route of Iron Oxide Nanoparticles

Iron oxide nanoparticles were synthesis by reverse micelle method. X-ray diffraction technique and vibration sample magnetometer were applied to characterize the produced samples at different conditions and parameters for synthesis route. There is no significant difference between samples prepared at 5°C and room temperature except a better crystalline at room temperature. The molar ratio of water to surfactant (w parameter) and concentration of the salt solution on size and magnetic properties of nanoparticles have been investigated. Increasing w leads to producing particles with larger size i.e. for w=16.83, 11.22, and 5.6, particles size are 15.22, 11.66 and 10.5 nm, respectively. The size of nanoparticles are in the range of 9 to 20 nanometers

One parameter control of the size of iron oxide nanoparticles synthesized in reverse micelles

Iron oxide nanoparticles were synthesized via reverse micelle methods. The initial iron concentration was varied, while maintaining all other parameters constant, in order to investigate the effect of the iron concentration on the resultant iron oxide nanoparticle size. Increasing the iron concentration from 0.125M to 0.5M yielded an increase in average nanoparticle diameter from 4.71 to 7.95 nm, as measured by transmission electron microscopy. Three other concentrations between 0.125M and 0.5M showed corresponding size variations, all with statistical significance. Magnetic characterization by vibrating sample magnetometry and powder x-ray diffraction was performed to verify proper phase and material. Further insight into the reverse micelle method was acquired along with the ability to tune the nanoparticle size.

Synthesis of gold-coated iron nanoparticles by a reverse micelle method

Synthesis of gold-coated iron nanoparticles by a reverse micelle method

Synthesis and characterization of core–shell type Fe 3O 4 nanoparticles in poly(organosilsesquioxane)

The core–shell type Fe 3O 4 nanoparticles in poly(organosilsesquioxane) (Fe 3O 4@OcTS) were prepared by one-pot synthesis using reverse micelle method. The as-prepared ferrofluid droplets with average size 4–15 nm were in situ encapsulated via polycondensation of molecularly self-assembled octenyltrimethoxysilane (OcTS). The dynamic light scattering and transmission electron microscopy investigations on coated magnetite nanoparticles revealed uniform size of spherical shape and having thin and transparent shells. These nanoparticles showed redispersibility in non-polar solvents without agglomerations due to coated by a layer of hydrophobic shells. The thermogravimetric analysis and infrared spectroscopy suggested the existence of core–shell type. X-ray diffraction confirmed magnetite cores. The superconducting quantum interference device (SQUID) showed that they exhibited superparamagnetic behavior at 300 K and ferromagnetic at 3 K.

Raman scattering spectra of CdS nanocrystals fabricated by a reverse micelle method

AbstractRaman scattering (RS) spectra of CdS nanocrystals (NCs) fabricated by a reverse micelle method were studied and were analysed using a phonon confinement model. One broad and red‐shifted RS peak due to the LO phonon confined in CdS NCs was observed. The RS spectra were calculated using a phonon confinement model with the NC sizes estimated from the optical absorption spectra. The calculated RS spectra as suming that the NCs have the wurtzite structure reproduce the experimental spectra better than those assuming zincblende structure, which is consistent with the result of transmission electron microscope (TEM) observations. Our finding indicates that the crystal structure of the nanocrystal can be determined by the analyses of Raman scattering spectral shape. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Synthesis and magnetic properties from Mn-doped CdS/SiO2 core–shell nanocrystals

Mn-doped CdS nanocrystals were synthesized via the modified reverse-micelle method and then a CdS/SiO2 core–shell structure was prepared under hydrolysis of tetraethyl orthosilicate (TEOS) without any coupling agent. Basing on the method, four typical samples with different Mn2+ ions concentrations were fabricated. The observations of morphology and microstructure display well-monodispersed core–shell nanoparticles with a diameter of about 20 nm. Electron paramagnetic resonance investigation reveals four kinds of distinct Mn2+ centres with different local structures in these samples. The magnetic field dependence of magnetization (M–H curves) of these samples was measured at a constant temperature of 4 K using a superconducting quantum interference device magnetometer. The results indicate that different distributions of Mn2+ ions in CdS/SiO2 core–shell nanocrystals lead to diversiform magnetic properties. Some possible origins are presented for these magnetic phenomena, especially for ferromagnetic characteristics.

Nano-sized PdO loaded SnO 2 nanoparticles by reverse micelle method for highly sensitive CO gas sensor

A reverse micelle method was investigated for preparing nano-sized PdO loaded on SnO 2 nanoparticles. PdO–SnO 2 nano-composite was prepared by precipitating Pd(OH) 2 and Sn(OH) 4 inside a reverse micelle. The microstructure and the gas sensing properties of obtained nanoparticles were investigated. Although the particle size of SnO 2 was as same as ca. 10 nm at each observed sample, the particle size of PdO got larger as increasing with loading amount of PdO because of agglomeration of PdO nanoparticles each other. As a result of the gas sensing measurement, it was found that the particle size of PdO on SnO 2 nanoparticle influences the gas sensing property closely. That is, the sensor response declined gradually with increasing the particle size of PdO although the maximum of the sensor response was obtained in PdO = 0.1 mol%. In this method, small amount of PdO loading can be achieved as compared with PdO-loaded SnO 2 sensor prepared by the conventional impregnation method.